[webkit-changes] [WebKit/WebKit] a8c0b8: Disable RespondToThermalPressureAggressively by de...

[bnham]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: a8c0b8ffdaf70de2ab49cc33db5955e7cc1766bb
      https://github.com/WebKit/WebKit/commit/a8c0b8ffdaf70de2ab49cc33db5955e7cc1766bb
  Author: Ben Nham <nham at apple.com>
  Date:   2025-01-31 (Fri, 31 Jan 2025)

  Changed paths:
    M Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

  Log Message:
  -----------
  Disable RespondToThermalPressureAggressively by default
https://bugs.webkit.org/show_bug.cgi?id=286776
rdar://143918242

Reviewed by Sihui Liu.

In 287858 at main I added the RespondToThermalPressureAggressively preference and enabled it by
default. However, this doesn't work as expected for a couple of reasons:

1. `HAVE_APPLE_THERMAL_MITIGATION_SUPPORT` is only enabled for visionOS. So even non-aggressive
thermal mitigation was doing nothing on iOS. After defining this and enabling this on iOS, we
realized aggressive mitigation causes a MotionMark regression, so it can't be enabled as-is.

2. On visionOS, the system is in charge of throttling the global framerate for all processes when it
detects thermal pressure. So if we were to then also throttle the frame rate in response to thermal
pressure in WebKit specifically as we do in 287858 at main, that could lead to something like 1/4 the
normal frame rate on webpages. That's not what we want.

For now, let's disable this preference while we refine the policy.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:

Canonical link: https://commits.webkit.org/289621@main



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